1. Field of the Invention
This invention relates to a cyclohexane derivative useful as a liquid crystal material. More particularly, it relates to a liquid crystalline compound having an alkenyl group at the end of its molecule and a liquid crystal composition containing the compound.
2. Description of the Related Art
Display elements utilizing liquid crystals have been broadly used for watches, electronic calculators, etc. These liquid crystal display elements are those utilizing the optical anisotropy and the dielectric anisotropy of liquid crystal substances. Liquid crystal phases include nematic liquid crystal phase, smectic liquid crystal phase and cholesteric liquid crystal phase, and among the above phases liquid crystal display elements utilizing nematic liquid crystal phase have been most broadly and practically used. Such display elements include those of TN (twisted nematic) mode, DS (dynamic scattering) mode, guest-host mode, DAP mode, etc., corresponding to the electro-optic effect applied to liquid crystal display, and as the liquid crystal substances utilized for the respective display elements, those exhibiting liquid crystal phases within a temperature range as broad as possible in the natural state are preferred. A large number of liquid crystal compounds have already been known, but at present, there is no single liquid crystal substance satisfying such conditions, but several kinds of liquid crystal substances or non-liquid crystal compounds have been mixed to be practically used. These substances are required to be stable to moisture, light, heat, air, etc. In particular, recently, there has been an increasing importance of substances having a low optical anisotropy, as a material for liquid crystal display element for active matrix mode represented by thin film transistor (TFT) mode. Further, it has been required for the liquid crystal material that its compatibility with a number of already existing liquid crystal materials is as large as possible at low temperatures.
The following compounds have so far been known as compounds similar to those of the present invention: ##STR2##
These compounds, particularly (I), (II), (III), (VI) and (VII), have been reported to have a large dielectric anisotropy value (.DELTA..epsilon.) and a low viscosity and exhibit an effect of lowering the threshold voltage without raising the viscosity. However, according to research of the present inventors, it has been found that the .DELTA..epsilon. value is comparatively small and the threshold voltage cannot be sufficiently lowered.